[FE] Add warning about potential performance implications when CSP namespace is updated

Why are we doing this work

When an administrator designates a CSP group through Admin > Settings > Security and compliance > Compliance and security policy group, we need to display a confirmation modal that warns the users about the current Beta status of the feature and that it may incur load on the system.

Relevant links

• https://docs.google.com/document/d/1afDyag9Aatl-6gsb1NQ7h9_8n6JHQGOmQEIOmLGwLuI discussion from our weekly @ 2025-08-05

Non-functional requirements

• Documentation:
• Feature flag: Modals should be hidden behind security_policies_csp (the whole admin CSP UI control currently is, too).
• Performance:
• Testing:

Implementation plan

• frontend TBD

Verification steps

TBD